Stereofluoroscopic apparatus



15, 1935# J. w. M. DU MoND 2,0635989 STEREOFLUOROSCOPIC APPARATUS uFiled Feb. a, 1952 4 sheet-sheet 1 s .4o .45 lINVENTOR- Dec.'l5, 1936.J. w. M. DU MOND STEREOFLUOROSCOPIC APPARATUS 4 Sheets-Sheet 2 FiledFeb. 8, 1932 INVENToR l J. w. M. Du MoND f 2,063,989

STEREOFLUOROSCOPIC APPARATUS Dec. 15, 1936.

4 sheets-sheet 3 A Filed Feb.l a, 19523- FIG. 7

9 INVENTOR LVW wwf.

Uec l5,v 1936. J. w, M. D U MoND STEREOFLUOROSCOPIC APPARATUS med Feb s1952 4 Sheets-Sheet 4 FIG I0 DESIRED IIVIAGE INVISIBLE IINDESIIIED IMAGECUT OFF IMAGE INVISIBLE IMAGE VISIBLE THRESHOLD UF VISIBILITYFLUORESCENT INTENSITI VOLTAGE FIG. I1

INVENTO'R Patented- Dec. 1 5, 1936 UNITED STATESA PATENT OFFICE tsTEREoFLUonoscorlc APPARATUS Jesse W. M. Du Mond, Pasadena, Calif.

Application February 8, 1932, Serial No. 591,654-

10 Claims.

My invention` relates to improvements in stereoiluoroscopic X-rayapparatus; and the objects of my improvement 'are to aord substantiallydistortionless stereoscopic projection of Rntgen images, to provide foraccurate measurement of such images and vtolsimplify the constructionand manipulation of the apparatus.

Some mathematical considerations are neces- I sary to an adequateunderstanding of the probtion, we must have lems involved in eliminatingdistortion in stereofluoroscopic images. Fig'. l of the accompanyingdrawings is a schematic illustration of a stereouoroscopic arrangement,in which I and 2 represent the focal points of two separate X-raysources, 3 and 4 the pupils of the eyes of an observer, 5 a iiuoroscopicscreen, 6 an object to be examined, and l the stereoscopic image oi'Athe l object.

Having reference to the lettering of Fig. 1, let:

e Jinterpupillary distance r=f= interfocal distance (gwen) Bobject-screen'distance wen) P F- tube-screen distance g1 i =imagescreendistance v ge-screen distance (to b x F tube-screen distance found)x=that value of x which makes io=1 S|=the longitudinal scale ratio=small distance in depth` of image (to 'b'e corresponding distance indepth of object found) S3=the lateral scale ratio= A small distancemeasured laterally in image (to be corresponding distance measured inobject found) l The rays from the two images on `the screen to the twoeyes cross at the image andform two similar triangles. tubes crossthrough 'ie object and form two similar triangles. The base-line d iscommon to the two systems. It is easy to show that:

In order that there shall beno depth distor- AFor this condition, onsolving for E T'x' we obtain: Y

- x=r+p(1fr) Y This s'js the ratio oi' the eye-screen distance to thetube-screen distance which must obtainif Also the rays from the two (Cl.Z50-34) there is to be no depth distortion. It depends on p, therelative position of the object. Hence, it is evident that for anextended object the distortion cannot be eliminated over all partsunless 1:1.-

If we solve Equation (1) for without the restriction that O shall equalunity weobtain:

o=r|p(1-r) (2'1) The longitudinal scale ratio `Si in the notation of thedifferential calculus is do l that is to say, the ratio of twocorresponding4 small elementary lengths measured in the direction ofdepth, one being in the image land the other in the object. To obtainthis we have only to diierentiate the Equation (2.1) according to therules of the differential calculus regarding i and o as the variables,but remembering that p is a function of o, namely WTV-r); A

Fig. 2 shows vthe curves of depth distortion for iive typical cases ofinterpupillary distance ranging from 55 to 'l5 mm. Fig. 3 shows thecurves of lateral distortion for the same cases of interpupillarydistance; both of these curves are computed for a value oi' :c such thato shall be unity when the object is one-fourth as far from the screen asare the focall spots (p=0.25). A fixed interfocal distance of 65 mm. isassumed. It is also assumed that the center of the object to be picturedis one quarter as far from the screen as are the focalspots. It isevident that for an observer with an interpupillary distance of 55 mm.the lateral dimensions of the image will be only about ninety-fivepercent natural'scale, even when the depth distortions have beenminimized by proper choice of the ratio Similarly, for an observer withan interpupillary distance of 75 mm. the lateral dimensions will bemagnified to about four percent greater than natural scale.

From all of the foregoing it follows that distortionless stereoscopicprojection can be achieved only by keeping F equal to E and f equal toe. Means to this end are suggested in lU. S. Patent #1,735,726 to F.Bornhardt. These include a mechanism for holding F always equal toE(x=1) and for varying the interfocal distance to match theinterpupillary distance of thev observer. To the latter end in theBornhardt patent two separate X-ray tubes are to be employed, and thespacing of these tubes from one another is to be made adjustable in suchmanner .as to provide the necessary range of interfocal distances.. Thissuggested solution of the problem is however impracticable, for thesimple reason that it is practically impossible to build X-ray tubes ofthe requisite power small enough in diameter to permit of interfocalspacing equal to interpupillary spacing. The limiting factor is the coldelectron emission, which takes place even in the highest vacua. Theminimum diameter of tube .envelope compatible with the requisiteelectrical functioning is greater than human interpupillary distances.A

In view' of the above considerations, my invention includes the use of aduplex tube with fixed interfocal spacing.L together with aninterpupillary compensator with an adjustment adapted to give the eyepupils lan optically effective virtual separation equal to the giveninterfocal distance. It also includes means for holding the ratio :cequal to 1. It further' includesa novel shutter adapted to excludeparallax and other errors of vision, and also means for accuratelycalipering the stereoscopic image. Still further advantages and novelfeatures will appear from the following description. l

Fig. 4 is a top view of a'representatlve embodiment of my invention.Fig. 5 is an enlarged rear view of the interpupillary compensator mechaynism. Fig. 6 is a front elevation of the device. Fig. 7 is a partialview ofthe compensator and shutter mechanism. Fig. 8 is an enlargeddetail view of the tube, and Fig. 9 shows schematically a preferred stoparrangement for narrowing the X-ray beams. Fig. 10 shows in frontelevation and Fig. 11 in section an alternative compensator design.Finally. Fig. 12 illustrates diagrammatically the shutter action.Similar numbering refers throughout to similar parts.

Referring now to Fig. 4, I is a duplex X-ray tube with focal spots 2,coolers 5 and filament leads I0 connected to the filaments associatedwith the respective focal spots.Y The filament current supply is derivedfrom the two transformers 6, the high tension supply from thetransformer with split secondary 1. Between the two secondary windingsare connected a D.C. and an A.,C. milli-ammeter. The latter indicatesthe total current supplied to the two laments, since its deiiectlon isindifferent to the direction of ow of current. The D. C. instrumentshould preferably be of the typewith zero in the middle of the scale,permitting the indication of current in either direction. The tubes arebalanced when this meter gives zero deflection. As the instruments aregrounded, they present no danger to the operator.

It is of course important that the two focal spots should be of nearlyequal intensity, although the requirements are not exacting. Thefilaments are Virtually connected in parallel (through their respectivetransformers) to the same voltage source, and there is therefore afavorable tendency toward stability of balance due to the positivethermal coeicient of tungsten filaments. A single filament controlrheostat serves to establish the balance, and it is hereby necessary toobserve only a single instrument for zero reading.

The tube is mounted on the support' I6. This carries a system ofaperture stops (to be later described) which is controlled by the lmobsI1. To I6 are linked the arms I2 and I4. To the outer ends ofthese armsis linked the arm I5. 'Ihis in turn carries the four-pole synchronousmotor 2I, which drives the shutter mechanism requisite tostereofluoroscopic viewing. The motor is mounted in an annular openingin the arm I5, and is held in position by the setscrew 22.

The. shutter is brought into phase with the X-ray sources by rotatingthe motor in its annular opening. The phasing process 1s as follows: Adiaphragm opaque to X-rays is placed over one of the sources. The motoris then rotated bodily until the eye on the same side as the obscuredsource sees a perfectly dark iield all over the screen. The set-screw 22is then clamped down. 'I'his method is far superior to that ofdisconnecting one of the tubes electrically, as in the latter case theconsequent dissymmetry of load shifts the phase of the single operatingtube away from that which it will have when both tubes are operating.

The arm I2 in its middle portion takes the form of a rectangular frame,in which is pivoted the iiuorescent screen I I. To this screen isaiilxed the tongue I3, which is linked to the middle oi' the arm I4.

The arms I2, I3, I4, I5, together with supportv I6 form a doubleparallelogram system which serves at once to keep the screen IIequldistant from the focal spots and the eyes of the observer (whilepermitting the usual variation of tube' screen distance), and to keepthe screen at all times parallel to the X-ray tube and the shutter.

Figures 4, 5, 6 and 7 show an embodiment of the interpupillarycompensator. The shutter casing 23carries la support 28, to which are.pivoted the prism casings 29.

The pivotal members Il! are aiiixed to the two casings 29, and areretained in rotatable relation to the support 28 by means of the nuts 39and the spring washers 3B.'

The spacing of the pivots is equivalent to the interfocal spacing of thetube. In the casings 29 are carried the .prisms 30, so disposed that the'center of the upper plane reecting surface of each prism coincides withthe pivotal axis, and that the lower plane reflecting surface of eachprism falls within the eld of vision of the observers eye. Thesefeatures are best illustrated by Fig. 7. l

Referring now to Fig. 5, the casings 29 are provided with inwardlyprojecting tongues 32, which pass under the head of a thumbnut 33. ThisA 1 a,ocs,9se

thumbnut is providedwith a shank which is threaded into the boss 28a ofthe; support v 2l. Spring 35 and washer I4 press tongues 32 upwardagainst the thumbnut. On turning the thumbnut,

are. provided with slots 3l (see Figs. 6 and 7). Y

The observersees the screen through these slots,

- and as they are but slightly wider than the pupils 'flecting surfaces.

he must adjust their spacing to interpupillary distance to obtain aclear view.

The bridge of theA observers nose rests in the nosepiece 36. This fixeshis eyes with respect to the'eye-slots 31 and guards against errors ofparallax. The pivots'of the parallelogram system should have suillcientfriction to guard againstl accidentalsllppage. lUnder thesecircumstances the observer finds no difliculty in maintaining his eyesin fixed relation to the optical system.

-An alternative compensator design is shown in Figures 10 and 11, ofwhich, the first is a front elevation and the second a section on the'dotted lines I I of Fig. 10. The functioning of this arrangement isthroughout similar `to the 'one just described, but instead of prismsfour mirrors are provided. These mirrored surfaces 30 can readily bemade' of such size as to afford a larger field of vision than canconveniently be provided by means oi prisms. -To vthis end, the upper orobjective plane reflecting surfaces are made very much larger than thelower or ocular plane re- The path of the light rays is indicated inFig. 11 by arrowed lines.

. running under conditions similar to those of the- '75 The shutterdesign is as follows: The four-pole synchronous motorv2l carries on itsframe the shutter casing 23. This casing is supported at its outerend\by the arm 24 (see Fig. 6), which is integral with the motorsupporting ring lia (which in turn is integral with the arm l5). Mountedon the motor shaft is the cylindrical shutter 42 (seen in section inFigs. 'l. and 1l). This shutter it not supported at its outer end, butterminates in the knob 2l, used for phasing purposes. As is well-known,a stereoucroscope will give either a-stereoscopic" or a"pseudoster'oscopic image, according `as the shutter is phased to admitlight induced by the right-hand focal y spot `to the left eye and thatinduced by the left spot to the right eye, or vice versa. As the formercase introduces grave distortions, the latter is preferred (and isthesubject of the considerations based on Fig. 1). If the motor shouldhappen to so step into phase as to give the former case, slight pressureon knob 26 will cause it pole and correct this.

The/'shutter 42 is pierced with four rectanguf lar openings in themanner indicated inFig. 1,

one pairA of openings being onset by 90 on the circumference of theshutter tube with respect to the other pair. The action of the shutterwith respect to one cycle of alternating current-is illustrated in Fig.A12. This vdiagram is self-explanatory. The curve of uorescent intensityis obtained in the following manner: A small sample of the iluorescentscreen to be used is glued to a disc (near its periphery) rotating onthe shaft of a four-pole synchronous motor operated at the frequency tobe employed. -Xrays from a tube stereoduoroscope are allowed to fall onthe rotatto slip 'a fined regions on the periphery'of the disc withinwhich the fluorescence of the' screen sample isv distinctly visible.This angle ofvi'sibility is measured and the opaque arc of the shutteris designed to match it.

The feasibility of the cylindrical shutter design which is'part. of myinvention depends on the fact that there are finite intervals ofinvisibility of the screen between succeeding halfing disc. There thenappear two quite well dey cycles, during .which the ilumination is belowthe I threshold ofv vision. These intervals are due partly to lthe factthat X-ray intensity is nearly proportional to the square of thesinusoidal applied voltage. The voltage sufiicient to excite visi-vbility on the screen is thus not attained until a considerable fractionof the half cycle has elapsed. If it were not for the effectively darkintervals, the unrescent image would not appear uniformly brilliantfromtop to bottom, because of the passage of the opaque shutter portionsinto the fleld of view at the back-side of the shutter. The foregoingconsiderations hold for practically any X-ray intensity; since thevisibility of the unwanted image at the moment of cut-oil or openingdepends on the degree to which the eye has already been excited "by theproper images just previous.

The cylindrical shutter design presents thev great advantage of easyadaptability to the eyes and the bridge of the nose. It enables veryclose approach of the eyes to the shutter mechanism.' thusaffording awide angle of vision while at the same time allowing for properproportioning of light and dark intervals.

An embodiment of the duplex X-ray tube which forms a partl of thisinvention is shown in Figs. 4 and L8. The targets 2 are sealed into theglass envelope i in the usual manner. The cathodes 3 are of conventionaldesign. However, one cathode terminal takes the form of the stem 4,which is affixed to the opposite target by means of the set-screw 4a.'I'he other terminal (which .is insulatd in any suitable manner from 4)is indicated schematically by line I0. This passes out throughase'aladjacent to the target in the manner shown in Fig. 4. The target facesare turned away from mutual parallelism just enough to permit the coneof X-rays from each focal spot to illuminate the-required field on thescreen. The cathodes are4 placed as nearv to their respective targets aspossible, consistent with complete illumination of the screen. Theproximity of the bell-shaped cathode shields the glass envelope frombombardment by electrons reflected and diiused after collision with thetarget. Such electrons otherwise tend to build up charges on the glasswall which might eventually cause puncture of they glass. Moreoven due'to the- I-Iittorf effect, the tube will operate on less rigidvconnected to the opposite anode, .the requisite i number of lglass sealsis reduced to a minimum.

Moreover, the axial arrangementof'all parts affords great simplicity inmanufacture.v

A most important feature of thistube design is that it utilizes to thefull the potential developed D bythe high-tension transformer, due toplacing one of the-cathode terminals. at the potential of .the oppositetarget.` We're this not the case, twice the amount' of secondary windingwould be required on the high-tension transformer. This would be farmore expensive than the use of two distinct filament secondaries. asrequired in connection with the present invention (see wiring diagram ofFig. 4).

l/Theapplication of aperture stops in the present invention isillustrated schematically in Fig.

9. In the first half of this figure the stops are -shown in nearlyclosed position, in the second half fully opened. These stops 4I may beoperated in the conventional manner (by means of levers connected toknobs in front of lthe apparatus, shown at I'I in Fig. 4). In thepresent invention two sets of stops, one for each X-ray source, areemployed. The inner stops of each pair overlap fully in the wide openposition. This is required by practical space limitations. The X-raybeams should be focused on the middle of the screen, as indicated by thedotted lines in the figure; the fields of the two beams then overlapcompletely, as required for proper stereoscopy.

A most important feature of` the present invention as a whole is that itprovides in practical form distortionless stereoscopic projection. Allthe novel elements described and illustrated contribute essentiallytoward this end. The ultimate object in the elimination of distortion isto enable the exact measurement of the position of objects within thebody being viewed, as well as their` dimensions in breadth and depth.

I provide for such measurement in the callper` ing arrangement I8, I9,shown in Figures 4 and 6; Reference numeral I8 indicates a rod a1:-Vtached to the frame of the screen I I. The two objects I9 are swivellingcaliper feelers of the type commonly usedv on machine-shop heightgauges. As is well known, such feelers may be adjusted for length andswiveled in all directions on loosening the single thumbnut which servesto. secure them to the supporting rod. For complex determinationsadditional feelers and supporting rods may be employed. The imageappears in space before the screen. It is a simple matter to set thefeeler tip on any point in the image; a plurality of such settings willserve to fix with great accuracy the dimensions and position of anyobjectIY or series of objects within the fee'ler supports might also beattached to someY part of the machine without the interposition of rodsI8. Also, within the scope of the invention, other measuring devicesthan those here sug- -gested might be so attached to the machine as' tobe interposed in the image field. The essential feature is that themeasuring arrangement be a part of the stereofluoroscopic apparatus,

that it be adaptedto contact portions of the image before the screen,and that, such contacts once established, distances may be. measured orread off after the lights in the observing room` have beenturned on andthe' image hasv disappeared.

The importance of such accurate determinations in fluoroscopic images asare made possible and practicable by the present invention isselfevident. For example, the precise location of a foreign. object inthe human body at a moments notice will greatly facilitate the work ofphysician and surgeen. n

It is to be' understood that the scope of my invention is not limited tothe particular combination of elements herein set forth. 'In particular,the term shutter is to be understood broadly in connection with myinvention. Any device adapted to select at the proper moment the imageto be viewed by a giveneye and to exclude from the other eye the sameimage, and vice versa, falls within the broader meaning intended incertain of the appended claims. I therefore use therein the term ,imageselector", as covering broadly all such devices, including shutters oflthe general type herein described. The term screen hereinafter employedrefers to such fluorescent screens as are commonly employed in the artand to any devices which serve a similar purpose. The term"interpupillary compensator is self-explanatory, and is to beunderstood-in its broadest sense.

The principles of stereofiuoroscopic apparatus, particularly withrespect to image selectors acting in synchronism with the X-ray sources,are understood in the art, and need not be further set forth here. Itisof course assumed that selector and sources are connected to a commonsource of alternating current.

Reference is hereby made to an article entitled The technic ofstereofluoroscopy in the magazine Radiology dated December 1932 for amore extended explanation of the mathematical and technical features setforth in these specifications. The content of this article is: to beconsidered as a supplementary part of these specifi'- cations althoughthe article is not essential for completeness of disclosure.

I claim:

1. A stereofluoroscopic'apparatus comprising: two X-rayA sources;supporting means for said X-rayesources; a iiuoroscopic screen gpositioned to receive radiations from said sources; supporting meanssecured to said screen and comprising a movable arm pivotally secured to'said firstnamed supporting means; an image selector positioned forviewing images on said screen produced by said radiations; supportingmeans secured to said selector and pivotally securedto lsaid movablearm; and link means connecting said selector supporting means and'saidfirstnamed supporting means inl a parallelogram arrangementy lwherebythe ratio of selector-screen distance to soudce-screen distance ismaintained constant during movement of said screen toward and away fromsaid X-ray sources.

Y2. The invention set forth in claim 1, said link means being providedwith connection to said screen whereby said screen is maintained in aparallel position with respect to said two X-ray f sources duringmovement thereof toward and away from said sources.

3. The invention set forth in claim 1, said screen being pivotallydisposed on said movable ^arm, and said link means being pivotallysecured to said screen to position said screen in parallel relation tosaid two X-ray sources upon movement of said movable arm to causesaidscreen to be moved toward or away fromsaid sources.

4. In a stereofluoroscopic apparatus, the combination comprising: twoX-ray sources having 5. Thecombination set forth in claim 4, saidinterpupillary compensator comprising: two spaced pairs of reflectingsurfaces, the reecting surfaces of each pair comprising an objectivereiiecting surface and an ocular reflecting surface disposed in parallelplanes, the objective reiiecting surfaces of each of said pairs beingpositioned to receive light along two spaced axes from said screen andreflect the same toward the respective ocular reflecting surfaces andsaid ocular reflecting surfaces being positioned to direct said lightalong two spaced axes, respectively parallel to said first-named axes tothe respective eyes of an observer, and comprising in addition, meansfor altering the inter-axial spacing of said ocular reflecting surfaceswhile maintaining the ifnteraxial spacing of said objective reectingsurfaces constant.

6. The combination set forth in claim 4, said of said ocular mirrorswhile maintaining the inter-axial spacing of said objective mirrorsconstant.

7. A stereoiiuoroscopic apparatus comprising: two spaced AX-ray sources;a iluoroscopic screen positioned to receive radiations from saidsources;

means for alternately energizing said X-raysources with alternatehalf-waves derived from a common source of alternating current to causealternate visible excitation of said screen byeach of said sourcesduring a portion of the half-,wave excitation thereof while providingblank periods between alternate visible excitations of said screenduring which the intensity of radiation received by saidscreen is belowthe threshold value for visibility; means for binocular observation ofsaid screen comprising movable shutter means disposed between theobservers eyes and the screen; and means for moving said shutter meansto positions alternately fully masking and fully unmasking said screento each eye in synchronism with and throughout substantially the entireperiod of alternate visible excitations of said screen andinstereoscopic relation and for moving said shutter means from maskingposition to unmasking position during one of said blank periods and formoving said shutter from unmasking position to masking position duringthe succeeding blank period.

8. Animage selector for use in stereoiiuoroscopic observations 4inconjunction with a fluoroscopic screen and two spaced and alternatelyenergized X-ray sources, comprising: a shutter casing; a shutter.rotatably mounted within said casing and provided with two axiallyspaced pairs of openings in the side wallsth'ereof, the openings of eachpair being diametrically opposite and axially alined with each other andthe two pairs of openings being disposed at to each other"with respectto the rotation of said shutter; means for synchronously rotating, saidshutter with respect tothe alternate energization of said twoXray.sources so as to cause said respective pairs of openings toalternately aline in viewingrelation with respect to said screen, saidcasing being provided with axially spaced aperture means positioned toregister with the respective pairs of openings in the shutter when insaid viewing relation; and an interpupillary compensator associated withsaid image selector adapted to give the eyes' or the observer anoptically effective virtual separation equal to the interfocal spacingof said X-ray sources.

An image selector forl use in stereouoroof openings in the side wallsthereof,.the openings of each pair being diametrically opposite andaxially alined with each other and the two pairs of openings beingdisposed at 90 to each other with' respect to the rotation of saidshutter;

.means for synchronouslyrotating said shutter with respect to thealternate energization of said two X-ray sources so as to cause saidrespective pairs of openings to alternately aline in viewing relationwith respect to said screen, said casing being provided 'withaxiallyspaced aperture means positioned to register with the respectivepairs of openings in the shutter when in said viewing relation; Vand aninterpupillary compensator comprising two spaced pairs of reectingsurfaces, the reflecting surfaces of each pair comprising an objectivereflecting surface and an ocular reflecting surface disposed in parallelplanes, the objective reflecting surfaces of each of said pairs beingpositioned to receive light l along two spaced axes from said screen andreiect the same toward the respective ocular. reflecting surfaces andsaid ocular'reecting surfaces being positioned to direct said lightalong two spaced axes respectively, parallel to said iirstnamed axis Vtothe respective eyes ofthe' observer; and means for altering theinter-axial spacing of said ocular reecting surfaces while maintainingthe inter-axial spacing of said objective reecting surfaces constant,the respective ocular reflecting surfaces being disposedin position toregister with respective pairs of openings in said shutter.

10. An electrical circuit for use in stereo'iiuoro-A scopy, comprising:two separate X-ray sources provided with thermionic cathodes; a `highpo- -tential transformer provided with an energized primary and with asecondary electrically connected to said X-ray sources and having anelectrically central portion maintained at substan-` tially groundpotential, an alternating current ammeterI inserted in series with saidsecondary in said ground potential portion for indicating the root meansquare value of the sum of the' two currents supplied to said two X-raysources named ammeter indicating the total energy dissipated in the twoX-raysources, and said secondnamed ammeter indicating the degree ofinequality of the energy dissipated in the two X-ray sources. r

' JESSE W. M. DU MOND.

